This invention relates to an improved process for the manufacture of shaped articles from a water-hardening material that has been reinforced with networks of fibrillated organic films.
The term "water-hardening material" as used herein refers to a mixture of a dry or substantially dry binder and water, optionally containing aggregates, that can be hardened or bound into a solid rigid mass by reaction between the binder and water. The term also applies to the hardened material after setting. Suitable binders include, for example, various types of cement, gypsum and other similar materials such as Portland cement, aluminum cement, plaster of Paris and anhydrite.
The use of both man-made and natural reinforcing fibers in a water-hardening material to make shaped articles is well known. The fibers may be either randomly distributed throughout the material, or incorporated as layers of loose fibers. Reinforcement may also be provided by incorporating a mat or fibers in such articles.
Continuous processes are known for the manufacture of articles made from water-hardening material incorporating fibrous reinforcement such as asbestos-cement products. However, it is now known that asbestos fibers constitute a serious health hazard to persons either engaged in or in proximity to the manufacture of asbestos-cement products, and those persons working with (such as cutting or shaping) the manufactured asbestos-cement products. For this reason many attempts have been made to devise substitutes for asbestos-cement products having equivalent mechanical properties and comparable costs, but these efforts have for the most part failed.
It has been proposed to make shaped articles of water-hardening materials reinforced by layers of stretched fibrillated organic films, and promising results have been achieved. But conventional manufacturing techniques such as used in the manufacture of asbestos-cement, including the use of rotary mixing equipment to homogeneously incorporate the reinforcing fibers into the water-hardening material, cannot be used with fibrillated organic films. Rather, time consuming and costly hand building techniques have been used which are not conductive to continuous mass production.
It is therefore an object of this invention to provide a continuous process for the manufacture of shaped articles of reinforced water-hardening materials, which process is flexible both with respect to the content of reinforcing material that may be utilized and the composition of the final article formed. It is a further object of this invention to provide a continuous process for the manufacture of shaped articles comparable or superior to asbestos-cement with respect to both physical properties and cost.